Varuna - 20000
Artist's conception of
Varuna - TNO (20000) Varuna
20000 Varuna is a large classical Kuiper Belt object
(KBO). It previously had the provisional designation 2000 WR106 and has
been precovered in plates dating back to 1953. Under the International
Astronomical Union's 2006 draft proposal for the definition of a planet,
Varuna would be labelled a dwarf planet if it were proven to be spherical.
The size of the large KBOs can be determined by simultaneous
observations of thermal emission and reflected sunlight. Unfortunately,
thermal measures, intrinsically weak for distant objects are further hampered
by the absorption of the Earth atmosphere as only the weak ‘tail’ of the
emissions is accessible to Earth-based observations. In addition, the estimates
are model-dependent with the unknown parameters (e.g. pole orientation
and thermal inertia) to be assumed. Consequently, the estimates of the
albedo vary resulting in sometimes substantial differences in the inferred
A recent thermal model estimates the size at 936 +238/-324
km. This estimate is based on earlier results (900 +129/-145) and (1060
Orbits of Varuna (blue)
and Pluto (red)
Varuna is classified as a classical trans-Neptunian
object and follows a near-circular orbit with a semi-major axis of ~43
AU, similar to that of Quaoar but more inclined. Its orbital period is
similar to Quaoar at 283 Earth years. The graph shows the polar view (top;
Varuna’s orbit in blue, Pluto’s in red, Neptune in grey). The spheres illustrate
the current (April 2006) positions, relative sizes and colours. The perihelia
(q), aphelia (Q) and the dates of passage are also marked. Interestingly,
the orbits of Varuna and Pluto have similar inclination and are similarly
oriented (the nodes of both orbits are quite close).
At 43 AU and on a near-circular orbit, unlike Pluto
which is in 2:3 orbital resonance with Neptune, Varuna is free from any
significant perturbation from Neptune. The ecliptic view illustrates the
comparison of Varuna's near-circular orbit with that of Pluto (highly eccentric,
e=0.25), both similarly inclined.
Varuna has a rotational period of approximately 3.17
hours (or 6.34 hours, depending on whether the light curve is single or
double-peaked). Given the rapid rotation, rare for objects so large, Varuna
is thought to be an elongated spheroid (ratio of axis 2:3), with a mean
density around 1g/cm³ (roughly the density of water ice). Examination
of Varuna's light curve has found that the best-fit model for Varuna is
a triaxial ellipsoid with the axes a,b,c in relations: b/a = 0.63 ? 0.80,
c/a = 0.45 ? 0.52 and a bulk density of 0.992 g/cm³. Since the
discovery of Varuna, another, even larger, rapidly rotating (3.9 h) object
(136108) 2003 EL61 has been discovered, also thought to have an elongated
The surface of Varuna is moderately red (similar to
Quaoar) but exceptionally dark (albedo<0.04) compared with other large
classical Kuiper Belt objects, suggesting that the surface is largely devoid
of ice, although small amounts of water ice have been detected on its surface
- 20000 Varuna
More Wikipedia Pages
diameters and albedos. Retrieved on 2006-11-08.
Lightcurves Lacerda P., Jewitt D. Dentisities Of Solar
System Objects From Their Rotational Lightcurves", accepted to AJ Dec.
and Centaur Colors. Retrieved on 2006-11-08.
Grundy, W. M.; Noll, K. S.; Stephens, D. C. (2005).
"Diverse albedos of small trans-neptunian objects". Icarus, 176: 184-191.Preprint
Jewitt D, Aussel H, Evans A (2001). "The size and albedo
of the Kuiper-belt object (20000) Varuna". Nature411
on the Author's site.
E. Lellouch, R. Moreno, J. L. Ortiz, G. Paubert, A.
Doressoundiram and N. Peixinho (2002). "Coordinated thermal and optical
observations of Trans-Neptunian object (20 000)Varuna from Sierra Nevada".
Astronomy & Astrophysics 391: 1133-1139.Preprint
Jewitt D, Sheppard S (2002). "Physical
Properties Of Trans-Neptunian Object (20000) Varuna". Astronomical
Journal 123 (April): 2110–2120.Preprint
L. Rabinowitz, K. M. Barkume, M.
E. Brown, H. G. Roe, M. Schwartz, S. W. Tourtellotte, C.
A. Trujillo (2005), Photometric Observations Constraining the Size,
Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized
Object in the Kuiper Belt, The Astrophysical Journal (2006), 639, Issue
2, pp. 1238-1251 Preprint
on arXiv (pdf)
Licandro J, Oliva E, Di Martino M (2001). "NICS-TNG
infrared spectroscopy of trans-neptunian objects 2000 EB173 and 2000 WR106".
& Astrophysics 373 (July): 29-32L.